Antenna having variable beamwidth achieved by variation of source width



Sept. 20, 1966 G. M. RANDALL ETAL 3,

ANTENNA HAVING VARIABLE BEAMWIDTH ACHIEVED BY VARIATION OF SOURCE WIDTH Filed Sept. 16, 1963 5 Sheets-Sheet 1 lo l4 FIG. 4 FIG. 3

INVENTORS GRANT M. RANDALL J A. ALGEO Sept. 20, 1966 G. M. RANDALL ETAL. 3,274,602

ANTENNA HAVING VARIABLE BEAMWIDTH ACHIEVED BY VARIATION OF SOURCE WIDTH Filed Sept. 16, 1963 5 Sheets-Sheet 2 FIG. 9A

FIG. 8A

INVENTORS GRANT M. RANDALL JERRY A. ALGEO FIG. ll

Sept. 20, 1966 G. M. RANDALL ETAL ANTENNA HAVING VARIABLE BEAMWIDTH ACHIEVED BY VARIATION OF SOURCE WIDTH Filed Sept. 16, 1963 5 Sheets-Sheet 5 FIG. 98

FIG as FIG. l0

SIGNAL SOURCE GI 72 72 INVENTORS GRANT M. RANDALL Y JERRY A. ALGEO B Sept. 20, 1966 RANDALL ETAL 3,274,602

ANTENNA HAVING VARIABLE BEAMWIDTH ACHIEVED BY VARIATION OF SOURCE WIDTH Filed Sept 16, 1963 5 Sheets-Sheet 4 FIG. |2

92 g lOO INVENTORS FIG. l3 GRANT M. RANDALL JERRY A. ALGEO p 20, 1966 G. M. RANDALL ETAL. 3,274,602

ANTENNA HAVING VARIABLE BEAMWIDTH ACHIEVED BY VARIATION OF SOURCE WIDTH Filed Sept. 16, 1963 5 Sheets-Sheet 5 R- T\ I I u FIT- l.. l I no "i l '0 l H I I 'I L.--

AGENT United States Patent O 3 274 602 ANTENNA HAVING VARIABLE BEAMWID'IH ACHIEVED BY VARIATION OF SOURCE WIDTH Grant M. Randall, Whittier, and Jerry A. Algeo, Buena Park, Califl, assignors to North American Aviation,

Inc.

Filed Sept. 16, 1963, Ser. No. 309,002 3 Claims. (Cl. 343-762) This invention relates to a variable beamwidth antenna; and more particularly to an antenna whose radiation and reception patterns can be easily changed.

BACKGROUND It is well known that radar is widely used, and that radar systems may be designed for a number of purposes. Basically, in all radar systems, radar energy is transmitted from an antenna to strike a target; whereupon the energy reflected by the target is then caught, and is directed to reception circuits that provide desired information about the target. This information is used in various Ways, depending upon the purpose of that system.

One operational mode of radar is the searching for, and the locating of, a target, such as an airplane. When the target has been located, the operational mode may be changed, so that the radar station can follow the movements of the target. The above modes of operation are known as searching and tracking respectively.

In the searching mode of operation the radar beam should cover a large area; so that any, and all, targets will be locatedwhereas in the tracking mode of operation, the radar beam should cover a smaller area; so that it may more precisely follow each movement of a specific target. This is analogous to using a wide-lens camera to find a target; and then switching to a telescopiclens to study the target.

The above modes of operation require radar beams of circular cross-section; but there are times--as for example when searching for a boat-when the radar beam should be narrow in elevation, and broad in azimuth; while at other times the beam should be broad in elevation, and narrow in azimuth.

As indicated above, radar may be used for still other purposes; these other purposes frequently requiring beams of still other shapes, such as skewed cross-sections.

As will be explained later, the pattern of the radar beam is determined by the radar antenna.

The above discussion indicates the desirability of having several different beam-patterns, to be used for the different modes of operation.

One solution to this problem is to use a plurality of antennas-each one designed for a particular mode of operation, and producing a particular beam-pattern. This becomes impracticable, particularly in airborne usage, because the additional weight of the plurality of antennas is a severe disadvantage.

Another solution to thisproblem would be to have an arrangement whose beam-pattern could be changed for the different modes of operation. While this approach has been used, the prior-art solutions have not been very satisfactory.

OBJECTS AND DRAWINGS It is therefore the principal object of the present invention to provide an improved antenna, whose beampattern may be changed as desired.

The attainment of this object and others will be realized from the following specification, taken in conjunction with the drawings of which FIGURE 1 shows an elementary antenna;

FIGURE 2 shows the beam-pattern produced by the antenna of FIGURE 1;

FIGURE 3 shows a horn-type antenna;

3,274,602 Patented Sept. 20, 1966 ice FIGURE 4 shows the beam-pattern produced by the antenna of FIGURE 3;

FIGURES 5 and 7 show variable-beam-pa-ttern hornantennas;

FIGURE 6 shows the beam-patterns produced by the antennas of FIGURES 5 and 7;

FIGURES 8a and 8b show other variable-beam pattern antennas with two different aperture-size control block settings;

FIGURES 9a and 9b show apertures of the embodiments of FIGURES 8a and 8b respectively;

FIGURES l0 and 12 show other variable-beam-pattern horn-antennas;

FIGURE 11 shows another way of controlling the beam-pattern produced by the antennas of FIGURES l0 and 12; and

FIGURES 13 and 14 show other variable-beam-pattern antennas.

INTRODUCTION Radar energy is generally of a relatively high frequency, the energy being known as microwave energy because the wavelength of the radar energy is so short. In order to transmit this energy from place to place, it is generally conducted through hollow metallic tubes, known as waveguides, which have carefully-specified dimensions.

If the end of the waveguide is open to the air, the radar energy will be emitted from the open end; and the open mouth of the waveguide is then a transmitting, or a radiating, antenna. This open-end antenna will transmit radar energy in a particular pattern; most of the energy continuing straight ahead, while some of the energy is transmitted at a slight angle to the longitudinal axis of the antenna. If a graph is made to show the distribution of energy, it turns out to be a rounded-end petal-like formation known as a lobe.

If the antenna is relatively large compared with the wavelength of the radar energy, the lobe will be relatively long and narrow; whereas if the antenna is relatively small compared with the wavelength of the radar energy, the lobe will be relatively short and wide.

Since the wavelength is determined by the radar system, the beam pattern may be controlled to a limited extent by flaring the end of the waveguide to produce a divergent horn, whose open month then acts as the antenna.

It will be realized that if the antenna is to produce a broad-lobed beam-pattern, as is desired in the searchmode, the antennas dimensions should be relatively small; whereas if the antenna is to produce a narrowlobed beam-pattern, as is desired in the track-mode, the antennas dimension should be relatively large. Thus, a suitably-flared horn can provide either of the desired beam patterns.

It should be noted at this time that the angle of the lobe-like beam-pattern is known as the beamwidth. Thus, a wide petal-like lobe has a large beamwidth; while a narrow petal-like lobe has a small beamwidth. Therefore, a lobe-pattern for the search mode has a wide beamwidth, whereas a lobe-pattern for the tracking mode has a narrow beamwidth.

It has been found that an antenna of the above-described horn-type is relatively inefficient. A higherefficiency antenna may be produced by placing the abovedescribed horn-antenna at the focal-point of a concave length of the energy passing through the waveguide.

nation originating at its focal point is reflected outward into space by the concave surf-ace of the dish, the outwardly radiated pattern forming the secondary illumination, since it is used to illuminate the target. Ordinarily, the dish has a parabolic configuration.

One prior-art approach to variable beam patterns controlled the area of the dish by having extensible vanes that slide in and out to decrease and increase the dishs diameter. While this approach does produce different beamwidth patterns, it is extremely ineflicient for the following reason. When the extensible vanes are extended to provide a large-diameter dish, each portion of the dish and each'portion of the extensible vanes receives primary illumination; and the large-diameter dishand-vanearrangement reflects radar energy to produce a narrow secondary-illumination lobe-pattern. When, however, the vanes are withdrawn, only the dish receives primary illumination; and, since the dish is smaller than the dish-and-vane combination, it now produces a broad secondary-illumination lobe-pattern.

Unfortunately, the radar energy that originally impinged upon the extended vanes is now wasted. In addition, the wasted energy is radiated backward and sideward, rather than forward. This wasted energy often strikes other objects, and is reflected back to the radar system, where it frequently interferes with the desired operation. Thus, this solution to a multi-mode radar antenna is not completely satisfactory.

It is a characteristic of an antenna that it can transmit energy; and that it can also receive incoming energyand that its transmission-pattern is similar to its reception-pattern. Thus, an antenna that concentrates its transmitted energy into a narrow-beamwidth lobe patternwhen used to receive energy, is more sensitive to energy originating in the same narrow-beamwidth lobepattern. This conforms to the theory of reciprocity.

SYNOPSIS The basic concept of the present invention is to pro duce different lobe-patterns by changing the size of the horn-mouth. This inventive concept takes several forms; one form using hinged-vanes that may be moved angularly to product different-sized antenna apertures; another form using blocks that slide forward or backward in order to change the size of the aperture; and another form using auxiliary waveguides that may be disabled or made operative, in order to change the aperture-size. Still another arrangement causes a variable-aperture antenna to primary-illuminate only desired areas of a reflector dish.

DESCRIPTION OF THE INVENTION FIGURE 1 shows a microwave waveguide that comprises a hollow tube having a cross-section whose shape and dimensions are determined primarily by the wave- As the energy is emitted from the open end of the waveguide, the beam-pattern in the horizontal plane takes the general form of lobe 12 of FIGURE 2. It will be noted that lobe 12 is relatively short and wide.

Referring now to FIGURE 3, it will be seen that main-waveguide ,10 now terminates in a flaring hornlike portion 14. As the energy is emitted from the enlarged open end of portion 14, the beam-pattern takes the form, in the horizontal plane, of lobe 16, of FIG- URE 4; the lobe 16 being longer and narrower than lobe 12. Since the vertical dimension of the antenna-aperture is the same in FIGURES 1 and 3, the beamwidth in the vertical plane would be the same in each case.

Thus, as previously discussed, the beamwidth of the lobes are determined by the size of the antenna-aperture.

One form of the present invention is shown in FIGURE 5. Here main-waveguide 10 has attached to it a variableaperture horn-like portion 20, the drawing showing an arrangement whose horizontal dimension may be varied.

Portion 20 comprises fixedly-positioned upper and lower plates, 22 and 24; and two angularly-positionable sideplates 26 and 28. The angularly-positionable side-plates 26 and 28 are pivotably attached to the main-Waveguide 10 by means such as hinges 30, so that the horizontal size of the antenna-aperture may be variably'controlled.

One or both of the positionable side-plates may be pivoted, by any convenient means such as a magnet, gears, levers, pulleys, or the like.

When the positionable side-plates 26 and 28 are close together they produce the wide-beamwidth solid-line lobepattern 32 of FIGURE 6, this lobe-pattern being similar to the lobe-pattern of FIGURE 1; whereas when sideplates 26 and 28 are spaced apart, they produce the narrow-beamwidth dotted-line lobe-pattern 34 of FIGURE 4these lobe-patterns being in the horizontal plane.

In this way the lobe-pattern can be progressively controlled to produce the beamwidth desired for the particular mode of radar operation.

It will of course be realized that the side-plates 26 and 28 may be fixedly-positioned, and that the upper and lower plates 22 and 24 may be angularly positionable, as shown in FIGURE 7. In this case the radiation pattern would vary in elevation rather than in azimuth. Alternatively, all the .end-platees may be angularly positionable.

Under some conditions it may be undesirable to have hinged plates; in which case the arrangement of FIG- URE 8 may be used. In the cutaway illustration of FIGURE 8a, the main waveguide 10 terminates in a series of aperture-size control blocks 40 and 42 that are shown to be vertically-positionable. When blocks 40 and 42 are positioned outwardly as far as they can go, as shown in FIGURE 8a, the mouth of the antenna is relatively large, as shown in FIGURE 9a, so that the lobe-pattern in the vertical plane is relatively narrow.

In the cut-away drawing of FIGURE 8b, the blocks 40 and 42 have been positioned inwardly, so that the antenna opening is relatively small, as shown in FIG- URE 9b, to produce a broad-beamwidth lobe-pattern in the vertical plane.

In this way the beamwidth of the lobe-pattern can be controlled by positioning blocks 40 and 42 to achieve the desired beamwidth lobe-pattern. The blocks are preferably small and numerous, in order to provide a uniformly flared horn; and may be positioned by any suitable means, such as gears, levers, pulleys, etc. Moreover, their movement may be guided by having them slide along a tongue-and-groove arrangement as shown.

Of course, the antennamay be formed so that the blocks vary the horizontal dimension of the aperture, and .thus vary the beamwidth in the horizontal plane.

It will be noted that the arrangements thus far described are progressively adjustable, so that a wide variety of lobe-patterns may be produced.

There may be times when mechanical movement, such as shown in the previous drawings, is undesirable. In cases such as this, the horn-type arrangement of FIG- URE 10 may be used. Here main-waveguide 10 has an auxiliary-waveguide 60 attached thereto; the waveguides having a common wall 61. The two waveguides are connected by a slot 62 known as a coupling slot; and under certain conditions, when slot 62 is open, energy traveling along main-waveguide 10 will divide as shown by the arrows. In that case, depending upon the design, a portion of the energy will come out of each waveguide; thus producing a large-opening horn-type antenna that has a narrow-beamwidth lobe-pattern in the horizontal p ane.

Under other conditions, when the slot 62 is closed, all of the energy is emitted from the relatively small opening of waveguide 10, to produce a wide-beamwidth lobepattern in the horizontal plane.

,FIGURE 10 indicates one Way to open and close the coupling slot 62. Here a suitable number of electricallyconductive short circuiting pins 64 are shown positioned in the coupling slot 62. Under these conditions, shorting-pins 64 act as an electrical short circuit; and thus cause partition 61 to be effectively continuous. Since partition 61 is effectively continuous, the energy traveling through main-wave guide cannot enter auxiliary waveguide 60, and it is therefore emitted from only the opening of main waveguide 10.

Short-circuiting pins 64 may be Withdrawn, by suitable means, such as a magnet; under which conditions the coupling slot 62 is eifectively open. Now some of the energy passes from main waveguide 10 to auxiliary waveguide 60, and is emitted from the mouth of auxiliary waveguide 60. The energy is now emitted from both waveguides, 10 and 60; the increased aperture acting to form a narrow-beamwidth lobe-pattern.

It is known that the energy emitted from auxiliarywaveguide 60 has a different phase than the energy emitted from main-waveguide 10; and to correct this situation a suitable phase-shifter 70 is positioned in auxiliary-waveguide 60. This arrangement assures that the energy emitted from waveguides 10 and 60 will have the desired phase relation, so that the overall assemibly acts like a single large-aperture horn-type antenna. Alternatively, a suitable phase-shifter may be placed in waveguide 10, downstream of the coupling slot.

It will be realized that the arrangement of FIGURE 10 provides an antenna whose aperture-size may be controlled to either of two dimensions, and therefore its horizontal lobe-pattern may be changed in accordance with the mode of operation.

Moreover, the arrangement of FIGURE 10 avoids the mechanical problems associated with the previously-disclosed arrangements; and may be actuated quickly when this is desired.

FIGURE 11 shows a partial pictorial-and-schematic arrangement wherein the short-circuiting pins have been replaced by electrical components, such as varactor diodes, 72, whose operation is such that when suitably activated they act as a short circuit; and thus produce the same elfect as the short-circuiting pins 64 of FIGURE 10. A suitable signal source controls the operating state of the varactors. Thus, without any mechanical movement at all, radar energy may be emitted from main-waveguide 10, or from main-waveguide 10 and auxiliary-waveguide 60. This electrical arrangement also permits extremely rapid switching between the broad and narrow lobepatterns; a situation which may be highly desired when two modes of operation are being used on a time-sharing basis.

Of course, additional auxiliary-waveguides may be used on the same or different sides of the main waveguide, and the arrangement may be designed to split the energy in any desired proportion. Thus different-shaped, and different intensity variation beam-patterns can be produced.

The coupling-slot shown in FIGURES 10 and 11 is known as sidewall coupling-slot, because it is in the side-wall that is common to each of two side-by-side waveguides. Under other conditions, the two waveguides may have an above-below relation, and the coupling slot is then known as a top-wall coupling slot.

This arrangement is shown in FIGURE 12. Here the top wall of main waveguide 10 is contiguous with the bottom wall of auxiliary waveguide 80. Contiguous Walls, such as previously described, are present when separate waveguides are used, while a common wall is present when the structure is formed by an extrusion or a compositing process. The two coupling slots 82 and 84 in the contiguous walls permit a portion of the energy in main waveguide 10 to pass into auxiliary waveguide 80. Retractable short-circuiting pins 86 may be suitably positioned or withdrawn by means such as magnets, to either prevent or permit energy from being emitted from the aperture of the auxiliary waveguide 80.

Alternatively, the varactor-diodes of FIGURE 11 may be used to effectively break or complete the contiguous Walls.

This arrangement varies the beam-pattern in the vertical plane.

There are times when it is undesirable to use the relatively ineflicient horn-type antenna; and the more-efficient horn-and-parabolic-dish arrangement may then be used. There are also times when the radar system requires pairs of antennas, one pair being positioned vertically while the other pair is positioned in a side-by-side arrangement; and these may also be used in conjunction with a parabolic dish.

FIGURE 13 shows an arrangement for using a parabolic dish and two pairs of horn-type antennas; while still taking advantage of the present inventive concept. In FIGURE 13, four antenna structures 92, 94, 96, and 98, of the type shown in FIGURE 10 are assembled so that the emitting apertures are at substantially the focal point of the parabolic reflector (reference numeral) 100; FIGURE 13 showing the antennas of FIGURE 10 as having been rotated degrees into a vertical arrangement to produce a variable beamwidth pattern in the vertical plane.

Alternatively, the antenna structure of FIGURE 12 may be used, either oriented as shown in that figure, or else rotate-d through 90 degrees.

As shown, the horn-type antennas direct their energy at the concave surface of dish 100.

As has been explained, if the horn-type antennas have a relatively small aperture, the assembly produces a widebeamwidth primary-illumination lobe-pattern; and in FIGURE 13 this pattern would illuminate the entire dish-which would thereupon produce a narrow-beamwidth secondary illumination lobe pattern. Conversely if the horn-type antennas have a relatively large aperture, the assembly produces a narrow-beamwidth primaryillumination lobe-pattern; and in FIGURE 13 this pattern would illuminate only the central portion of the dishwhich would thereupon produce a wide-beamwidth secondary-illumination lobe-pattern.

In this way, the antenna assembly at the focal point of the dish can produce either a broad-beamwidth or a narrow-beamwidth secondary-illumination pattern.

This result is achieved as follows. From the previous discussion it is apparent that it is possible to use all of the apertures, or only the center-most openings of the antenna array of FIGURE 13. The four center-most openings, because of their relatively small dimensions, produce a broad-beamwidth lobe-pattern of primaryillumiuation that illuminates the entire concave surface of the parabolic dish. Since the primary-illumination illuminates the entire surface of the dish, the effectively large-diameter dish reflects the radar energy outward in a narrow-beamwidth secondary-illumination lobe-pattern.

When a broad-beamwidth secondary-illumination lobepattern is desired, the outer-most auxiliary horns are also used, by properly adjusting the short-circuiting structure of the antennas. At this time the relatively-large emittingarea of the combined horns produces a relatively narrow primary-illumination lobe-pattern that illuminates only the central portion of the parabolic dish. The effective small-diameter dish reflects the radar energy outward in a broad-beamwidth secondary-illumination lobe-pattern.

It is also possible to use the auxiliary waveguides of only one, two, three, or all four of the horns, so that any desired lobe-pattern may be produced, for either the transmission or reception of radar energy. With appropriate microwave feeding structures attached to the multihorn arrangement, a monopulse antenna radiation pattern having multi-mode-variable beamwidth capabilities can be produced.

Thus, by using the apparatus of FIGURE 13, it is possible to obtain a narrow-lobed, a wide-lobed, a skewed,

a paired, or other-shaped secondary-illumination patterns, which may be switched from one to another, depending upon the mode to be used. It should be noted that in this arrangement none of the radar energy is wasted, since all of it impinges on some portion of the dish.

The arrangement of FIGURE 13 permits the beamwidth to be changed in the vertical plane; or, if the hornassembly is rotated 90 degrees, to be changed in the horizontal plane. However, there are times when it is desirable to change the beamwidth in both planes, either separately or simultaneously.

This result can be achieved by the structure of FIG- URE 14, which shows an assembly comprising four main waveguides 102108, and eight auxiliary waveguides 110 124. Each waveguide is coupled to its adjacent waveguides by suitable coupling-slots and short-circuiting elements, so that energy can be introduced into selected auxiliary waveguides. By suitably energizing the various short-circuiting elements, energy can be emitted from selected apertures.

While twelve apertures are shown, four additional corner waveguides may be added for more symmetrical results. As previously indicated, the use of suitably-sized coupling-slots, apertures, phase-shifters, and the like, permit the assembly to provide radiation-patterns of wide diversity.

It is well-known by those skilled in the art, that the manner in which the dish is primary-illuminated controls the side-lobes that represent radar energy emitted in undesired directions. As previously indicated, the auxiliarywaveguide arrangement of FIGURES 10, 12, 13, and 14 can be designed so that the auxiliary waveguides have desired cross-sectional dimensions, shapes, etc.; and thus transmit desired amounts of energy in desired patterns. In this way the energy emitted by the main and auxiliary waveguides produces a primary-illumination pattern that minimizes the production of side-lobes; and thus produces a more desirable secondary-illumination pattern.

Although the invention has been illustrated and described in detail, it is to be clearly understood that the same is by Way of limitation; the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim: 1. In a horn-type microwave antenna having a main waveguide terminal horn portion, one open end of which is adapted to cooperate with an antenna dish and an opposite end of which is adapted to be connected to a feedhorn, variable aperture means comprising an auxiliary terminal horn portion, one end of which is open and adapted to cooperate with said antenna dish and an opposite end of which is closed, said auxiliary horn portion having one wall thereof contiguous with a wall of said main horn portion;

coupling slot means in said contiguous walls and intercoupling said main and auxiliary terminal horn portions in microwave circuit; and

switchable shortcircuiting impedance means mounted in said coupling slot means and oriented for selectively decoupling said intercoupled terminal horn portions.

2. The device of claim 1 in which said switchable short circuiting impedance means is comprised of at least a varactor diode adapted to be connected in circuit to an electrical signal source.

3. The device of claim 1 in which said switchable short circuiting means is comprised of retractable short-circuit pins.

References Cited by the Examiner UNITED STATES PATENTS 2,519,603 8/1950 Reber 343786 2,534,271 10/1950 Kienow 343786 X 2,735,069 2/1956 Riblet 33310 2,820,202 1/1958 Miller 333-73 2,918,673 12/1959 Lewis et al. 343786 3,160,887 12/1964 Broussaud 343-777 OTHER REFERENCES Reich et al.: Microwave Theory and Techniques, Van Nostrand, N.Y., 1953, p. 369.

HERMAN KARL SAALBACH, Primary Examiner.

M. NUSSBAUM, Assistant Examiner. 

1. IN A HORN-TYPE MICROWAVE ANTENNA HAVING A MAIN WAVEGUIDE TERMINAL HORN PORTION, ONE OPEN END OF WHICH IS ADAPTED TO COOPERATE WITH AN ANTENNA DISH AND AN OPPOSITE END OF WHICH IS ADAPTED TO BE CONNECTED TO A FEEDHORN, VARIABLE APERTURE MEANS COMPRISING AN AUXILIARY TERMINAL HORN PORTION, ONE END OF WHICH IS OPEN AND ADAPTED TO COOPERATE WITH SAID ANTENNA DISH AND AN OPPOSITE END OF WHICH IS CLOSED, SAID AUXILIARY HORN PORTION HAVING ONE WALL THEREOF CONTIGUOUS WITH A WALL OF SAID MAIN HORN PORTION; COUPLING SLOT MEANS IN SAID CONTIGUOUS WALLS AND INTERCOUPLING SAID MAIN AND AUXILIARY TERMINAL HORN PORTIONS IN MICROWAVE CIRCUIT; AND SWITCHABLE SHORTCIRCUITING IMPEDANCE MEANS MOUNTED IN SAID COUPLING SLOT MEANS AND ORIENTED FOR SELECTIVELY DECOUPLING SAID INTERCOUPLED TERMINAL HORN PORTIONS. 